By Nathan Koppel 

San Antonio is moving ahead with plans to annex as much as 66 square miles around it, a land grab that would add as many as 200,000 people to the city and potentially make it the nation's fifth-largest metropolis.

The San Antonio City Council this month voted in favor of conducting a fiscal analysis of the proposed annexation. The process requires further council approval and the annexation would take about four years to complete. City leaders say the move would allow San Antonio, currently the nation's seventh-largest city with 1.4 million people, to better manage growth and remain economically vibrant.

If the annexation occurs, San Antonio could break into the ranks of the top five biggest U.S. cities, behind New York, Los Angeles, Chicago and Houston and ahead of Philadelphia and Phoenix, now Nos. 5 and 6.

"Cities that do not grow run the risk of two things happening: They will lose control over development outside their boundaries, and they will lose control over their long-term finances," said San Antonio City Councilman Joe Krier.

But some residents of the unincorporated areas in line to be annexed are opposed, fearing they will be forced to pay higher taxes and receive little in return.

"No one ever wants to pay more taxes," said Mamerto Luzarraga, a 47-year-old real estate professional who lives in Alamo Ranch, a large community that could be swallowed up by the city. "One of the selling points of this community is that you live close to city amenities, but you get to pay reduced taxes."

Unlike many large U.S. cities ringed by smaller incorporated towns, especially in the Northeast and Midwest, San Antonio has room to expand, say urban planning experts.

It is already one of the nation's fastest-growing cities after steadily increasing its population and area during the past decades. San Antonio expanded from 262 square miles and 786,000 people in 1980 to 407 square miles and 1.1 million people by 2000. Its current size is 486 square miles.

San Antonio "should consider itself lucky," said Andrew Reschovsky, an annexation expert with the Lincoln Institute of Land Policy in Cambridge, Mass. He said many big cities have been weakened by losing affluent residents--and their taxes--to suburbs, and noted that annexation can be a potent tool for cities to effectively retain some of that population.

San Antonio's Department of Planning and Community Development has recommended annexing five areas, which total 66 square miles and are located to the north, east and west of the city limits. Most of the areas are in Bexar County.

Within 20 years of being fully annexed, the communities would cumulatively generate $77 million annually in added revenue for the city, according to projections by San Antonio's planning agency. It estimated whether tax revenue from the new residents would exceed the cost of providing them with services, such as police and fire protection.

Bexar County Judge Nelson Wolff, a former mayor of San Antonio, said he supports the proposed annexation plan and wishes the city would take in even more county land.

A majority of San Antonio's 10-member city council is expected to vote in favor of annexing some or all of the targeted land, council members and other city leaders said in interviews. The council is tentatively scheduled to vote in December 2015 on whether to annex three of the five targeted areas. It would vote in 2016 on the other two areas.

San Antonio's mayor also will get to cast a vote. Mayor Ivy Taylor, who was appointed to fill the unexpired term of Julián Castro after he left in July to become secretary of the U.S. Department of Housing and Urban Development, favors annexing all the targeted land, a spokesman said. Ms. Taylor hasn't said whether she plans to run in May's mayoral election.

City leaders who back the annexation plan say it is vital for San Antonio to capture tax revenue from its high-growth suburbs and to ensure those areas are developed in line with the city's building, zoning and water-conservation regulations.

Ron Nirenberg, another council member who supports annexation, said it is imperative that San Antonio centrally manage growth given that the metro area is expanding so rapidly and already faces challenges with traffic congestion and potential water scarcity.

"We have a challenge in making sure we don't have unbridled growth," he said. Earlier this year, Mr. Nirenberg was among the majority of city officials who voted 9 to 1 in favor of a separate annexation of 19 square miles.

The lone dissenting vote was cast by council member Shirley Gonzales. She also opposes the current, proposed annexation, believing San Antonio should focus instead on providing better services to inner-city neighborhoods like the ones she represents. "There are a finite amount of resources," she said. Still, she conceded, "most of the council is supportive" of annexation.

Other council members note that the city could improve inner-city services while absorbing new neighborhoods.

"I'm a big believer in healthy downtowns but one of the ways we have paid for that is with property taxes from developments far away from downtown," Mr. Krier said.

Stephen Klineberg, an urban planning expert at Rice University, said many city planners view annexation as a means to advance their inner-city goals. "When rich people go out into the suburbs that is where the money is," he said. "You can use that tax revenue to develop the urban core."

Write to Nathan Koppel at nathan.koppel@wsj.com